<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>外边距典型应用之行内元素和行内块元素水平居中</title>
    <style>
        .header {
            width: 900px;
            height: 200px;
            background-color: pink;
            margin: 100px auto;
            /* 要让行内元素或行内块元素水平居中， 只需要给它的父元素添加text-align: center即可！*/
            text-align: center;
        }
    </style>
</head>

<body>
    <div class="header">
        <span>
            里面的文字
        </span>
    </div>
    <div class="header">
        <img src="images/down.jpg">
    </div>
</body>

</html>